A power converter for outputting power from a small power-generating facility or a small storage battery to a system is known. Such a power converter is called the “power conditioner” or “system-interconnected inverter”. In this type of power converter, there is a need to reduce harmonics in AC power outputted to a system to maintain the quality of the AC power.
In apparatuses disclosed in JP-A-2000-152647, JP-A-2000-350467, JP-A-2000-333471, and JP-A-2001-8465, when an AC voltage of a system is lower than a DC voltage of a power source, only an inverter is driven, and when the AC voltage is higher than the DC voltage, only a booster circuit is driven. The booster circuit is controlled based on a current that flows through a reactor of the booster circuit.
In the conventional apparatuses, the booster circuit is controlled based on the reactor current. A current also flows from an input power source to an input-side smoothing capacitor. That is, the reactor current does not accurately reflect an output-side AC current. Therefore, it is difficult to reduce harmonic components in the AC output.
Further, in the conventional apparatuses, the AC current may be distorted when the control is switched between the inverter and the booster circuit. JP-A-2000-333471 discloses a technique for reducing the distortion. In the technique, the detected DC current value is corrected to correct the switching timing. However, the distortion is caused by a capacitive component and an inductive component in the circuit. Therefore, it is difficult to reduce the distortion to a sufficient level by using the technique.